At present, as a growing number of people use wireless local area networks (WLAN) to carry out data communication, the WLAN network load is continuously increased. Furthermore, as the number of uses is increasing, an obviously decreasing tendency may appear in the WLAN network efficiency, and this problem cannot be solved merely by increasing rate. Therefore, Institute of Electrical and Electronics Engineers (IEEE) organizes a 11ax task group (also known as high-efficiency WLAN group) dedicated to solving the problem of the WLAN network efficiency. As one of alternative technologies for solving the network efficiency, a parallel multi-user data transmission technology has drawn extensive attention and study.
At present, the parallel multi-user data transmission technology studied by the 11ax group includes a multi-user multiple-input multiple-output (MU-MIMO) technology (spatial domain multiple access), orthogonal frequency division multiple access (OFDMA) technology (frequency domain multiple access), and interleave-division multiple-access (IDMA) technology (code division multiple access) technology.
FIG. 1 is an exemplary diagram of a WLAN basic service set (BSS). As shown in FIG. 1, in the WLAN, an access point (AP) and a plurality of non-AP stations (non-AP STA) associated with the AP constitute a basic service set. The parallel multi-user data transmission as mentioned in the WLAN generally refers that a plurality of secondary nodes simultaneously transmit data to a primary node, which is referred to as an uplink multi-user (UL MU), or that a primary node simultaneously transmits data to a plurality of secondary nodes, which are referred to as downlink multi-users (DL MU). Generally, the primary node is an AP or a non-AP STA with special ability, and the secondary node is a general non-AP STA.
In a WLAN system, data transmission generally is random access, and there is no strict synchronous relationship. Therefore, to allow a receiver to successfully detect and receive data in a radio frame, the WLAN radio frame generally includes a physical layer frame header and a data payload, where the physical layer frame header further includes a training sequence and a physical layer frame header signaling, as shown in FIG. 2. The above training sequence is used by the receiver to detect starting of the radio frame, and carry out operations such as synchronization, gain control, channel estimation and so on, to assist in receiving the physical layer frame header signaling and the data payload. The physical layer frame header signaling generally is transmitted using a fixed format and indicates a transmitted parameter of the data payload, for example, information such as a modulation and coding scheme and a bandwidth of the data payload. In conclusion, the physical layer frame header is a combination of the training sequence and the signaling domain, which is designed for assisting in receiving the data payload.
With the development of WLAN, new technologies are continuously introduced into the WLAN standard, and thus the format of the above WLAN radio frame is also continuously changed. For example, 802.11a/g adopts the orthogonal frequency division multiplexing (OFDM) technology. To receive the OFDM data payload, the physical layer frame header needs to assist the OFDM in receiving the required training sequence and the physical layer frame header signaling. This format is currently referred to as a non-high-throughput format (non-HT format). MIMO and a bandwidth of 40 MHz are also introduced into 802.11n. The format of the radio frame is modified to adapt to these changes. This format is currently referred to as a high-throughput format (HT format). Technologies such as more advanced MIMO, larger bandwidth, DL MU-MIMO and so on are introduced into 802.11ac. The format of the 802.11ac is currently referred to as a very-high-throughput format (VHT format). To increase the efficiency, technologies such as OFDMA multi-user transmission, narrower OFDM sub-carrier spacing and so on are also introduced into the new generation of WLAN, and thus the frame format thereof is also changed, which is tentatively referred to as a high-efficiency format (HE format) at present.
The WLAN radio frame format is in continuous development, and is characterized by: (1) backward compatibility, where a WLAN device can decode a frame format defined earlier than a standard supported by the WLAN device, for example, a VHT station can transmit and receive frames with VHT, HT and non-HT formats, but a non-HT station can neither transmit nor receive a frame with HT or VHT format; (2) the frame format is in continuous development, where the basic structure of a frame still includes the physical layer frame header and the data payload, the physical layer frame header is a combination of the training sequence and the signaling domain, which is designed for assisting in receiving the data payload closely following physical layer frame header; and (3) to allow more types of stations to decode a control frame or control information, generally it is suggested to transmit the control frame or the control information using the non-HT format to ensure that the control information may be detected by new and old devices, for example, channel resource reservation information is transmitted using the non-HT format, which may better protect the data transfer from interference.
FIG. 3 is a schematic diagram of an uplink multi-user transmission procedure in the prior art. In the prior art, a UL MU transmission procedure is started by an AP by transmitting a trigger frame including scheduling and signaling indication, and an uplink multi-user transmits the trigger frame according to the content of the trigger frame. In this way, the problem of interference and synchronization between uplink multi-users is solved. The scheduling and signaling indication contained in the above trigger frame specifically indicates the length of the data transmitted by the station, the transmitted parameter, and a location of resource for uplink transmission. In addition, to enable the trigger frame to play a role in reserving channel resources and protecting the uplink multi-user transmission, the trigger frame is transmitted using a traditional frame format (non-HT format) or a traditional modulation and coding scheme, so as to ensure that traditional devices and other listening devices also can parse the reservation information in the trigger frame.
However, following problems exist in the trigger frame with the traditional format. (1) If a new frame format (HE format) is adopted for data transmission of the uplink multi-user, to ensure the synchronization, the uplink multi-user needs to measure the trigger frame and transmit a multi-user radio frame with an uplink HE format according to a measurement result. However, if the trigger frame uses the traditional format instead of the HE format, the training signal carried in the traditional format is designed to receive the data payload with the traditional frame format, which may ensure successful reception of the trigger frame but is insufficient to meet the training precision required for the multi-user transmission. As shown in FIG. 3, the trigger frame with the traditional format only carries a traditional training signal. In this case, if the trigger frame adopts the HE format, although the training precision or training requirements may be satisfied, it is impossible for a traditional terminal to decode the trigger frame, and it is impossible to acquire the channel resource reservation information from the trigger frame, and thus the traditional terminal may likely interfere with transmission of an HE terminal. (2) Upon receiving the trigger frame, the uplink multi-user needs to immediately carry out uplink transmission after a particular interframe space (IFS), and thus may have no enough time for data preparation. As shown in FIG. 3, after a short interframe space (SIFS), the STA1˜STA4 may likely be unable to prepare the uplink multi-user radio frame.
As can be seen from the above procedure, in the prior art, using a trigger frame is not able to complete transmission resources reservation and trigger multi-user transmission at the same time as satisfying the training accuracy required for uplink multi-user transmission, and it is impossible to ensure that a station will have enough time to prepare uplink data after receiving a trigger frame.
This section provides background information related to the present disclosure which is not necessarily prior art.